As you know, a WordPress post can usually be seen going to a link similar to this:
myblog.com/2014/03/27/sample-post/
There is no folder named 2014, 03, 27 or sample-post in the blog.
Until now, I used something like this: page.php?post_id=55.
How is WordPress and other sites (I think StackExchange sites do this too) doing this?
Not sure if you are asking how to do this, but it’s a setting in Settings > Permalinks. You would select the Day and Name option. This should automatically format your Post articles in this format.